Gas detection apparatuses for detecting gases are used in various fields. For example, gas detection apparatuses can be used to detect the concentration of a gas targeted for detection and acquire data for measuring an indoor or outdoor environment. Patent literature (PTL) 1, for example, discloses a gas detection apparatus that includes a near-infrared light source and a light detection unit and detects the concentration of a gas inside a gas cell by non-dispersive infrared (NDIR).
A gas detection apparatus that includes a waveguide for light, instead of a gas cell, is also known. PTL 2, for example, discloses a gas detection apparatus in which an optical waveguide layer forming a waveguide is in contact with a reactive film that reacts to a gas. The gas detection apparatus detects the concentration of the gas based on attenuation of light in the waveguide.